Stereotactic access devices and methods

ABSTRACT

This invention is directed to devices and methods for stereotactic access, and particularly to a frameless stereotactic access device for accessing a body cavity and methods therefor. In general, a stereotactic device may include portions or features for fixing the device to a portion of a patient&#39;s body, such as, for example, a skull, such that the device may be generally spatially fixed in relation to the patient&#39;s body or part thereof. The stereotactic device may also generally include portions or features for guiding a medical device or other device at a particular trajectory in relation to the patient&#39;s body or part thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of U.S. provisional patentapplication Ser. No. 61/525,911, filed Aug. 22, 2011, and entitled“STEREOTACTIC ACCESS DEVICE”, the contents of which are herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to devices and methods for stereotactic access,and particularly to a frameless stereotactic access device for accessinga body cavity and methods therefor.

BACKGROUND OF THE INVENTION

Stereotactic head frames have a long and proven history in neurosurgery.The two most commonly used are the Leksell (Elekta) and CRW (IntegraNeurosciences) frames. In these procedures, a frame is mounted to thehead by screwing pins directly against the patient's skull for fixationat four points. The head with attached frame are then imaged by CT orMRI to identify targets, either manually or more frequently withcomputerized software, in relation to the external frame. Since both theframe and target can be viewed on the images, the distance of the targetfrom given reference points on the frame can be measured in threecoordinates. Next in the OR, an arc apparatus is attached to the headframe and adjusted based on the previously measured coordinates anddesired trajectory. One in position, a guide is used to drill a holealong a trajectory to the target. These head frames are associated withhigh accuracy (1-2 mm) for reaching target structures, much of which isachieved by having a permanent fixation between the skull and guidebeing used for creating the cranial access. Unfortunately, the frame iscumbersome, uncomfortable for patients, and time intensive.

Frameless stereotactic procedures rely on registration of the patient'sskull using anatomical landmarks, skin fiducial, or bone fiducials to apre-acquired MRI or CT scan. In the operating room the orientation offiducial markers or skin surfaces is registered using stereoscopiccameras on the navigation system to a volume of brain images. Onceregistration is completed, the navigation system can show therelationship of any registered surgical instruments to patient's brainanatomy. The two major manufacturers of these neuronavigation systemsare Medtronic and Brainlabs. Both companies offer accessories whichattach to the patients bed to allow twist drill access to a target alonga defined trajectory. The drawback to these accessories(Medtronic—Precision Aiming Device and Brainlab Varioguide) are thatneither is directly attached to the patient's head, and therefore anymovement of the drill is not directly accompanied by a correspondingmovement of the head. Both systems require additional time and resourceto set up in the operating room. Finally, because skin fiducials aremovable in relation to the underlying skull, additional error may berealized from the registration alone.

SUMMARY OF THE INVENTION

This invention is directed to devices and methods for stereotacticaccess, and particularly to a frameless stereotactic access device foraccessing a body cavity and methods therefor. In general, a stereotacticdevice may include portions or features for fixing the device to aportion of a patient's body, such as, for example, a skull, such thatthe device may be generally spatially fixed in relation to the patient'sbody or part thereof. The stereotactic device may also generally includeportions or features for guiding a medical device or other device at aparticular trajectory in relation to the patient's body or part thereof.

In one aspect, a stereotactic access device includes a plurality ofmounting arms which may further include mounting devices or featuressuch that, for example, the stereotactic access device may be mountedsecurely to a patient's body or part thereof. In some embodiments, themounting arms may generally be adapted to provide a stable mounting ofthe stereotactic access device to a patient's body or part thereof. Forexample, many body parts have curved or irregular surfaces such thatstable mounting may be desirable. In an exemplary embodiment, themounting arms may form at least a stable plane such that when themounting arms are attached to the patient's body, the stereotacticaccess device may generally be spatially stable and/or attachedsecurely. In one embodiment, the stereotactic access device may includethree mounting arms which may form a stable plane. The mounting arms mayalso be adapted to conform to the contours of a patient's body or partthereof, such as, for example, a skull. The mounting arms may further beadapted to contour, for example, such that there may be access spacebetween the stereotactic access device and the patient's body and/orportion thereof. This may be desirable, for example, to manipulate amedical device and/or other device between the stereotactic accessdevice and the patient's body and/or portion thereof.

In another aspect, a stereotactic access device includes a mountingand/or guiding feature such that a medical device and/or other devicemay be mounted to or guided to the stereotactic access device such that,for example, the device may be retained at a particular orientationand/or spatial relationship to the patient's body or part thereof. Insome embodiments, the mounting and/or guiding feature may include arotatable portion, such as an orbitally rotatable and/or swivelableportion, such that the orientation of the portion may be changed withrespect to the patient's body, a portion thereof, and/or the rest of thestereotactic access device. In an exemplary embodiment, the mountingand/or guiding feature may include, for example, a rotating sphere whichmay further include a guide channel to, for example, receive a medicaldevice and/or other device.

In a further aspect, a stereotactic access device includes features foraiding in mounting, positioning and/or registering the position and/ororientation of the stereotactic access device, for example, in relationto the patient's body and/or portion thereof. In some embodiments, thestereotactic access device may include, for example, mounting hardwaresuch as, for example, screws, nails, bolts, pins, and/or any otherappropriate mounting hardware or combination thereof. For certaincurvatures and/or shapes of a body and/or portion thereof, spacersand/or other adjustment accessories, such as spacers between the end ofthe mounting arm(s) and the body, may be utilized such that a stableplane may be established with the stereotactic access device. Ingeneral, the mounting hardware may provide, for example, stable and/orsecure retention and/or fixation of the stereotactic access device to apatient's body and/or portion thereof, such as, for example, to a boneor soft tissue via, for example, mounting arms. In some embodiments, themounting hardware may also provide and/or act as, for example, fiducialmarkers for aiding in positioning and/or registering the position and/ororientation of the stereotactic access device, such as, for example,relative to the patient's body and/or portion thereof. For example, themounting hardware may be registered and/or imaged by a detectionmodality, such as, for example, magnetic resonance imaging (MRI), X-ray,computerized tomography (CT), ultrasound, and/or any other appropriatedetection modality or combination thereof.

In another aspect, a stereotactic access device is utilized in methodsfor accessing the interior of a patient's body at a particular locationand/or along a particular trajectory. In an exemplary embodiment, amethod for stereotactic access may include:

Step 1: After registration of the patient and navigation tools, astandard navigation wand may be used to determine and mark a rough entrypoint, and the patient may then be prepped. The navigation wand may thenbe inserted into the sphere of the stereotactic access device such thatthe surgeon may hold both devices, for example, with one hand.

Step 2: Using stereotactic navigation software, the surgeon may find thedesired entry point again and may then align the navigation wand withthe planned trajectory to a target. The surgeon may then slide thestereotactic access device down onto the patient's body and mountinghardware, such as, for example, three small titanium screws, may then besecured, for example, through the skin and into bone, such as, forexample, the skull. The wand may be used again to confirm thetrajectory, such as prior to locking the device in place.

Step 3: The surgeon may then remove the navigation wand and replace itwith, for example, one of several various sized drill adapters. A stabincision may also be made at the entry site under the stereotacticaccess device. A surgical drill may then be inserted along the lockedtrajectory and a twist drill hole may be created through, for example, abone such as the skull.

Step 4: The drill adapter may then be retracted to optionally allow, forexample, a bone screw or anchor to be placed under the stereotacticaccess device. The drill adapter may be made to fit into the bone screwor anchor's proximal end such that the threads of the screw may fallinto the hole created in step 3. A biopsy probe may also be passeddirectly through an appropriate adapter, for example, such as with itsown thumb screw, and may be used to acquire, for example, tissuesamples.

Step 5: For placement of probes or electrodes, the surgeon may securethe bone screw by securing it in, for example, the previously drilledhole.

Step 6: The stereotactic access device may be removed, for example, byunscrewing the three screws, and if any stab incisions were created,they may be closed using a single staple or suture. A Touhy-Borstadapter may also be threaded onto the proximal female luer of the bonescrew, which may allow applicators to pass through while ensuring asterile field.

In some embodiments, the stereotactic access device may also be left inplace after a hole is drilled. For example, a bone screw may connect tothe stereotactic access device such that a continuous sealed channel maybe established from the stereotactic access device through the bonescrew and into the body. A sealing cap and/or other sealing componentmay also be included to close off the introducing end of thestereotactic access device.

In other embodiments, the stereotactic access device may be left inplace and an introducer may be inserted into the channel of thestereotactic access device and into the drilled hole in the body. Theend of the introducer may further include a cap and/or a seal such thatthe channel may be kept sterile.

In some aspects, the stereotactic access device may be desirable as itmay generally be utilized with existing and/or standard practicenavigation devices, probes and/or systems, and may thus be adaptable toa diverse number of medical practices with very little additionaltraining and/or the need for specialized equipment. For example, thestereotactic access device may generally be compatible and/or becompatible via adapters to receive a standard navigation probe or wand,treatment devices, drills and/or other equipment used in stereotacticsurgery. Further, use of the stereotactic access device may generally beintuitive and aid in surgical usage with a minimal number of movingparts and/or components such that, for example, users may use thestereotactic access device with minimal difficulty, while still beinghighly versatile in application due to a universal use design.

The present invention together with the above and other advantages maybest be understood from the following detailed description of theembodiments of the invention illustrated in the drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1, 1 a, 1 b and 1 c illustrate a stereotactic access device insome embodiments of the present invention;

FIGS. 2-1, 2-2, 2-3, 2-4, 2-5 and 2-6 illustrate the steps of a methodof stereotactic access to a patient's body in some embodiments of thepresent invention;

FIGS. 3 and 3 a illustrate an example of a frameless stereotactic accessdevice;

FIGS. 3 b and 3 c illustrate an example of a bone anchor for use with aframeless stereotactic access device; and

FIGS. 4, 4 a and 4 b illustrate a frameless stereotactic access devicewith a sealed device introducer.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below is intended as a description ofthe presently exemplified devices, methods and materials provided inaccordance with aspects of the present invention, and it is not intendedto represent the only forms in which the present invention may bepracticed or utilized. It is to be understood, however, that the same orequivalent functions and components may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this invention belongs. Although any methods, devicesand materials similar or equivalent to those described herein can beused in the practice or testing of the invention, the exemplifiedmethods, devices and materials are now described.

This invention is directed to devices and methods for stereotacticaccess, and particularly to a frameless stereotactic access device foraccessing a body cavity and methods therefor. In general, a stereotacticdevice may include portions or features for fixing the device to aportion of a patient's body, such as, for example, a skull, such thatthe device may be generally spatially fixed in relation to the patient'sbody or part thereof. The stereotactic device may also generally includeportions or features for guiding a medical device or other device at aparticular trajectory in relation to the patient's body or part thereof.

In one aspect, a stereotactic access device includes a plurality ofmounting arms which may further include mounting devices or featuressuch that, for example, the stereotactic access device may be mountedsecurely to a patient's body or part thereof. In some embodiments, themounting arms may generally be adapted to provide a stable mounting ofthe stereotactic access device to a patient's body or part thereof. Forexample, many body parts have curved or irregular surfaces such thatstable mounting may be desirable. In an exemplary embodiment, themounting arms may form at least a stable plane such that when themounting arms are attached to the patient's body, the stereotacticaccess device may generally be spatially stable and/or attachedsecurely. In one embodiment, the stereotactic access device may includethree mounting arms which may form a stable plane. The mounting arms mayalso be adapted to conform to the contours of a patient's body or partthereof, such as, for example, a skull. The mounting arms may further beadapted to contour, for example, such that there may be access spacebetween the stereotactic access device and the patient's body and/orportion thereof. This may be desirable, for example, to manipulate amedical device and/or other device between the stereotactic accessdevice and the patient's body and/or portion thereof.

FIG. 1 illustrates an example of an embodiment of a stereotactic accessdevice 100. In some embodiments, such as illustrated, the stereotacticaccess device 100 may generally be a tripod and may include mountingarms 102, such as the three illustrated, which may provide a stableplanar platform when mounted to a patient's body. The mounting arms 102may also generally form a space 106 between the stereotactic accessdevice 100 and a patient's body. This may be desirable such that thearea may be freely accessed when the stereotactic access device 100 isin place on the patient's body.

In another aspect, a stereotactic access device includes a mountingand/or guiding feature such that a medical device and/or other devicemay be mounted to or guided to the stereotactic access device such that,for example, the device may be retained at a particular orientationand/or spatial relationship to the patient's body or part thereof. Insome embodiments, the mounting and/or guiding feature may includerotatable portion such that the orientation of the portion may bechanged with respect to the patient's body, a portion thereof, and/orthe rest of the stereotactic access device. In an exemplary embodiment,the mounting and/or guiding feature may include, for example, a rotatingsphere which may further include a guide channel to, for example,receive a medical device and/or other device.

In FIG. 1, the stereotactic access device 100 may include a mountingball 110, which may be retained in track 108. The mounting ball 110 maygenerally rotate in the track 108 such that the guide channel 111 may bealigned at the appropriate angle, such as illustrated in FIG. 1 a. Themounting ball 100 may thus retain another device, such as, for example,a navigation wand 200, relative to the patient's body 90, such asillustrated in FIG. 1 a. The mounting ball 110 may also include asecuring part or feature, such as, for example, a securing screw, suchthat the mounting ball 110 may be locked in a particular orientation,such as with the thumbscrew 112 illustrated in FIGS. 1 b and 1 c.

In a further aspect, a stereotactic access device includes features foraiding in mounting, positioning and/or registering the position and/ororientation of the stereotactic access device, for example, in relationto the patient's body and/or portion thereof. In some embodiments, thestereotactic access device may include, for example, mounting hardwaresuch as, for example, screws, nails, bolts, pins, and/or any otherappropriate mounting hardware or combination thereof. For certaincurvatures and/or shapes of a body and/or portion thereof, spacersand/or other adjustment accessories, such as spacers between the end ofthe mounting arm(s) and the body, may be utilized such that a stableplane may be established with the stereotactic access device. Ingeneral, the mounting hardware may provide, for example, stable and/orsecure retention and/or fixation of the stereotactic access device to apatient's body and/or portion thereof, such as, for example, to a boneor soft tissue via, for example, mounting arms. In some embodiments, themounting hardware may also provide and/or act as, for example, fiducialmarkers for aiding in positioning and/or registering the position and/ororientation of the stereotactic access device, such as, for example,relative to the patient's body and/or portion thereof. For example, themounting hardware may be registered and/or imaged by a detectionmodality, such as, for example, magnetic resonance imaging (MRI), X-ray,computerized tomography (CT), ultrasound, and/or any other appropriatedetection modality or combination thereof.

As illustrated in FIG. 1, the stereotactic access device 100 mayinclude, for example, screws 103, which may be mounted at the ends ofthe mounting arms 102. The screws 103 may be, for example, self-tappingsuch that they may, for example, thread themselves into a surface, suchas the patient's body. The screws 103 may also act as fiducials, asdiscussed above. For certain curvatures of the body and/or othersituations requiring adjustment of the apparent dimensions of themounting arms 102, spacers may be included, such as, for example, aboutthe screws 103 between the end of the mounting arms 102 and the body,such that they may, for further example, effectively lengthen themounting arms 102.

In another aspect, a stereotactic access device is utilized in methodsfor accessing the interior of a patient's body at a particular locationand/or along a particular trajectory. In an exemplary embodiment, amethod for stereotactic access may include:

Step 1: As illustrated in FIG. 2-1, after registration of the patientand navigation tools, a standard navigation wand 200 may be used todetermine and mark a rough entry point 92 on the patient's body 90, andthe patient may then be prepped. The navigation wand 200 may then beinserted into the sphere of the stereotactic access device 100 such thatthe surgeon may hold both devices, for example, with one hand.

Step 2: As illustrated in FIG. 2-2, using stereotactic navigationsoftware, the surgeon may find the desired entry point 92 again and maythen align the navigation wand 200 with the planned trajectory to atarget. The surgeon may then slide the stereotactic access device 100down onto the patient's body and mounting hardware, such as, forexample, three small titanium screws, may then be secured, for example,through the skin and into bone, such as, for example, the skull. Thenavigation wand 200 may be used again to confirm the trajectory, such asprior to locking the stereotactic access device 100 in place.

Step 3: As illustrated in FIG. 2-3, the surgeon may then remove thenavigation wand 200 and replace it with, for example, one of severalvarious sized drill adapters 310. A stab incision may also be made atthe entry site 92 under the stereotactic access device 100. A surgicaldrill 300 may then be inserted along the locked trajectory and a twistdrill hole may be created through, for example, a bone such as theskull, at the entry site 92.

Step 4: As illustrated in FIG. 2-4, the drill adapter 310 may then beretracted to optionally allow, for example, a bone screw or anchor 400to be placed under the stereotactic access device 100. The drill adapter310 may be made to fit into the bone screw or anchor's 400 proximal endsuch that the threads of the screw 400 may fall into the hole created instep at the entry site 92. A biopsy probe may also be passed directlythrough an appropriate adapter, for example, such as with its own thumbscrew, and may be used to acquire, for example, tissue samples.

Step 5: As illustrated in FIG. 2-5, for placement of probes orelectrodes, the surgeon may secure the bone screw 400 by securing it in,for example, the previously drilled hole at the entry site 92.

Step 6: As illustrated in FIG. 2-6, the stereotactic access device 100may be removed, for example, by unscrewing the three screws, and if anystab incisions were created, they may be closed using a single staple orsuture. A Touhy-Borst adapter 410 may also be threaded onto the proximalfemale luer of the bone screw 400, which may allow applicators to passthrough while ensuring a sterile field.

In some embodiments, the stereotactic access device 100 may also be leftin place after a hole at entry site 92 is drilled. For example, a bonescrew 400 may connect to the stereotactic access device 100 such that acontinuous sealed channel may be established from the stereotacticaccess device 100 through the bone screw 400 and into the body 90. Asealing cap and/or other sealing component may also be included to closeoff the introducing end of the stereotactic access device 100.

In other embodiments, such as illustrated in FIGS. 4, 4 a and 4 b, thestereotactic access device 100 may be left in place and an introducer400′ may be inserted into the channel 111 of the stereotactic accessdevice 100 and into the drilled hole at the entry site 92 in the body90. The end of the introducer 400′ may further include a cap and/or aseal, such as the sealing cap 410 as illustrated in FIG. 4, such thatthe channel 402 may be kept sterile. The insertable portion 404 may beretained in the guide channel 111. The insertable end 405 may further bethreaded to engage the drilled hole at the entry site 92. A device 500,such as a laser probe and/or other type of medical device, may then beinserted into the channel 402 through the introducer 400′ and into thebody through the entry site 92, as illustrated in FIG. 4 b.

Example of Construction of a Frameless Stereotactic Cranial Access Guide

In an example of a stereotactic access device, a frameless stereotacticcranial access guide (FIGS. 3, 3 a, 3 b and 3 c) includes 2 parts—Tripod100 and a bone screw 400. The tripod 100 (measuring for example 2.5″ indiameter and 1.25″ in height) may hold several adapters for variousnavigation wands, drills, and bone screws 400 (measuring for example1.5″ in diameter). Wherever the tripod 100 is located on the cranium,the feet may be seated to allow all three screws to have a solid hold tothe skull, due to the planar tripod body design. Space is providedbetween the patient's skull and the base of the sphere 110 to allowaccess to the incision/entry point. The sphere 110 press fits into thebody of the tripod 100 and swivels in all directions. The through hole111 in the sphere 110 may fit various adapters for several parts of theprocedure. The thumbscrew 112 is used to tighten and secure the sphere110 in a particular orientation once the desired trajectory is achieved.Three guide screws 103 are located on the tips 102 of the tripod 100 andmay secure to the skull and anchor the guide in its position over theskull, such as, for example, over the entry point.

It will be appreciated by those of ordinary skill in the art that thepresent invention can be embodied in other specific forms withoutdeparting from the spirit or essential character hereof. The presentdescription is therefore considered in all respects to be illustrativeand not restrictive. The scope of the present invention is indicated bythe appended claims, and all changes that come within the meaning andrange of equivalents thereof are intended to be embraced therein.

The invention claimed is:
 1. A system comprising: a stereotactic accessdevice comprising a tripod having three mounting arms forming a stableplanar platform with an access space, wherein each of the mounting armscomprises a respective securing device, and wherein the securing devicesare at respective distal ends of the mounting arms and are configured tothread into a bone of a patient, and a mounting guide having a guidechannel, wherein the mounting guide is retained in a track in thetripod, wherein distances between the mounting guide and the securingdevices are fixed, the mounting arms are arched to provide the accessspace, which is present between a distal side of the mounting guide andthe bone of the patient while the securing devices are secured to thebone of the patient, and each of the securing devices comprises arespective registerable fiducial in a fixed positional relationshiprelative to the tripod; and a bone screw configured to extend throughthe mounting guide and screw into the bone of the patient, and whereinthe bone screw comprises a channel through which a second device mayextend to enter the bone of the patient.
 2. The system of claim 1,wherein each of the securing devices comprises a respective self-tappingscrew.
 3. The system of claim 1, wherein the registerable fiducials aredetectable by a magnetic resonance imaging (MRI) system, an X-raysystem, a computerized tomography (CT) system, or an ultrasound system.4. The system of claim 1, wherein the guide channel is adapted toreceive a navigation wand.
 5. The system of claim 1, wherein themounting guide is a mounting ball.
 6. The system of claim 5, furthercomprising a locking screw adapted to lock the mounting guide in anorientation relative to the tripod.
 7. The system of claim 1, furthercomprising spacers at the ends of the mounting arms.
 8. The system ofclaim 1, wherein: the mounting guide is spherical shaped and swivels;the track is cup-shaped and receives the mounting guide; and themounting guide is press-fit into the track.
 9. A system comprising: astereotactic access device comprising a tripod having three mountingarms forming a stable planar platform with an access space, wherein eachof the mounting arms comprises a respective securing device, and whereinthe securing devices are at respective distal ends of the mounting armsand are configured to thread into a bone of a patient, and a mountingguide having a guide channel, wherein the mounting guide is retained ina track in the tripod, wherein distances between the mounting guide andthe securing devices are fixed, the mounting arms are arched to providethe access space, which is present between a distal side of the mountingguide and the bone of the patient while the securing devices are securedto the bone of the patient, and each of the securing devices comprises arespective registerable fiducial in a fixed positional relationshiprelative to the tripod; and a bone screw configured to (i) contact thedistal side of the mounting guide, or (ii) partially fit into a proximalside of the mounting guide, wherein the bone screw comprises a firstportion, an insertable portion, and a threaded portion, the firstportion remains on the proximal side of the mounting guide, theinsertable portion extends through the mounting guide, the threadedportion screws into the bone of the patient, and the first portion, theinsertable portion, and the threaded portion provide a channel throughwhich a device may extend to enter the bone of the patient.
 10. Thesystem of claim 9, further comprising a Toughy-Borst adapter configuredto (i) attach to a proximal side of the bone screw, and (ii) receive thedevice prior to the being received by the bone screw.
 11. A systemcomprising: a stereotactic access device comprising a tripod havingthree mounting arms forming a stable planar platform with an accessspace, wherein each of the mounting arms comprises a respective securingdevice, and wherein the securing devices are at respective distal endsof the mounting arms, and a mounting guide having a guide channel,wherein the mounting guide is retained in a track in the tripod, whereineach of the securing devices comprises a respective registerablefiducial in a fixed positional relationship relative to the tripod; anda bone screw connected to and disposed on a distal side of the mountingguide, wherein the bone screw has a threaded portion, which isconfigured to be screwed into a bone of a patient, and a channel throughwhich a second device may extend to enter the bone of the patient. 12.The stereotactic access device of claim 11, wherein: the mounting guideis spherical shaped and swivels; the track is cup-shaped and receivesthe mounting guide; and the mounting guide is press-fit into the track.13. The system of claim 11, wherein: the bone screw comprises a firstportion, an insertable portion, and a threaded portion; the firstportion remains on a proximal side of the mounting guide; the insertableportion extends through the mounting guide; the threaded portion screwsinto the bone of the patient; and the first portion, the insertableportion, and the threaded portion provide a channel through which asecond device may extend to enter the bone of the patient.
 14. Thesystem of claim 13, further comprising a Toughy-Borst adapter configuredto (i) attach to a proximal side of the bone screw, and (ii) receive thesecond device prior to the second device being received by the bonescrew.
 15. A system comprising: a stereotactic access device comprisinga tripod having three mounting arms forming a stable planar platformwith an access space, wherein each of the mounting arms comprises arespective securing device, and wherein the securing devices are atrespective distal ends of the mounting arms and are configured to threadinto a bone of a patient, and a mounting guide having a guide channel,wherein the mounting guide is retained in a track in the tripod, whereindistances between the mounting guide and the securing devices are fixed,the mounting arms are arched to provide the access space, which ispresent between a distal side of the mounting guide and the bone of thepatient while the securing devices are secured to the bone of thepatient, and each of the securing devices comprises a respectiveregisterable fiducial in a fixed positional relationship relative to thetripod; and a bone screw comprising a threaded portion and an insertableportion, wherein the threaded portion is configured to be screwed intothe bone of the patient, wherein the insertable portion is configured tobe retained in the guide channel, and wherein the bone screw furthercomprising a channel through which a second device may extend to enterthe bone of the patient.